[TenTec] It's getting cold. Perfect antenna weather for a OCF dipole

[Rick - DJ0IP / NJ0IP]

Ha Ha, love that Wade!
I don't want to fry anyone.
My goal here is to help people understand how to use these antennas in a
safe way that will not fry them.

First of all, let's ALL agree the definition of the word "fry".

When Jim said you fry the balun, my interpretation was, it gets so hot that
it self-destructs.
This includes things like wire insulation burning up, wires short
circuiting, and toroids cracking or even shattering.

In general, this is not happening on a large scale and most of the time it
does, it is a self-inflicted wound by the operator doing a dumb thing.

However baluns can indeed get hot, very hot, and hot means loss.  How much?
I don't know.  But in the antennas I've used, not hot enough to prevent me
from making lots of contacts and scoring relatively high scores in major
contests ("high" compared to others using any kind of single element wire
antenna).

If Jim was speaking figuratively, then I agree with him.  We are slowly
frying the balun but my mid-sized balun has been used for 4 years now
running 600w and SWR wise, nothing has changed.  So I'll just keep frying it
as I enjoy many more QSOs with it.

Wade, CMC is indeed a very significant problem with these OCFD antennas.
You have to pay special attention to how you feed them.
If you get sloppy, you get burned.

Here is what I suggest:  

For the transformation, use a 4:1 voltage balun, wrapped on a single
FT-240-61 core.  That only transforms the impedance, it doesn't do a thing
to stop the CMC.  

Then connect (directly to the voltage balun) a 1:1 Guanella balun wrapped
with 16 turns of RG-142 around a pair of FT-240-43 toroids stacked and glued
together.  Just outside the shack, insert another RF-choke.  You can try a
Maxwell at first, that might suffice.  Otherwise add another choke as
described above.  If you have a long run of coax, break it up in the middle
with another choke.  So far I have only used Maxwell chokes for this job and
I have been getting away with it.

The strength of the CMC varies significantly along the coax.  It is maximum
at half wavelength intervals and minimum at odd-quarter wavelength
intervals.  VF is 0.98 in this case, NOT 0.66.

So choose your overall length of coax carefully.
Try to get close to 1/4 or 3/4 wavelength; avoid half wavelength multiples
by at about 1/8 wavelength.

I'm 98% sure you can then run a kilowatt through the antenna without frying
the operator.

Sell your flamesuit.

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)


-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Wade Staggs
Sent: Tuesday, September 22, 2015 5:54 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] It's getting cold. Perfect antenna weather for a OCF
dipole

*Well my guess is that I am about to get really Slammed. We have used
several OCF Antennas. At 100 Watts, things are pretty good. My problems
appear anytime we try to go QRO. At a Kilowatt there doesn't seem to be any
magic trick, device or method to get rid of the Massive amounts of RF coming
back into the Shack. Some bands are better than others. My cure was to
install a Dipole at 126 feet long. Or 63 feet each leg. We feed it with
450 Ohm Windowed Line ( some call it Ladder Line. )  And use a Tuner rated
to do the job. Most OCF Antennas must use a Tuner anyway to get full band
coverage. So we just installed an antenna that will cover 80 through 6
Meters at Very Low Loss and Great SWR. Just Google " The Lure of Ladder Line
" to learn more. And Rick, please don't Fry me in Hot Transformer Oil for
giving my opinion... hi .. hi .. My antenna at Field Day, always out
performs the various OCF, Inverted L and all the others. This is an equal
playing field. Same Location. Limited to 100 Watts. You get my drift?*
*                                               73 from Wade/KJ4WS*


On Mon, Sep 21, 2015 at 4:35 PM, <km2km at twc.com> wrote:

> Mike,
>
>  I am late in picking up this thread, nevertheless I went through the 
> OCF dipole fever, modeled like mad (EZNEC), read the literature, and 
> like all of our antennas you have fans for everything from the 
> proverbial bed spring to the OCFD.
>
> IMHO: although they will claim multiple band resonance, the models 
> show "close but no cigar."  (I'll be slammed on this for sure.
>
> Then too, those commercial versions have baluns to make it match, and 
> in the end, the recommendation is to use a tuner.
>
> If you would like to OP on 30 meters, then make a dipole and hang it 
> as high as you can.
>
>
> Kris KM2KM
> MERSCHROD
> 123 Warren Road
> Ithaca, NY 14850
>
> ---- Mike Bryce <prosolar at sssnet.com> wrote:
>
> =============
> Gang,
>
> It's been way to quiet here.
>
> With fall only a week away and winter not too far behind, it's a great 
> time for antenna work.
>
> I'am going to out up a off center fed dipole.
>
> After reading pages after pages of information about this antenna it 
> seems to work differently depending to quite a few factors.
>
> Such as how high up, gauge of wire, insulated or not and of course the 
> feed point.
>
> From what I've read, 137' wire. Short end about 42'
>
> (All lengths are for example only!)
>
> Now according to W8JI, he suggest the short end should be 24'
>
> Has anyone built a OCF dipole to W8JI dimensions?
>
> According to his web page, the above feed point will get me 30 meters. 
> I'd love to put my Argonaut VI on 30 meters this fall.
>
> I've got the wire a good 4:1 current balun and a rainy Sunday.
>
> Mike WB8VGE
>
> Sent
> from my iPhone
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--
*Living one day at a time with Jesus as my Savior. But, still having Fun.*
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